The Endometrial Cycle (Menstrual cycle)

• In the endometrial lining of the uterus.

– Proliferative phase

– Secretory phase

– Menstruation

The Endometrial Cycle (Menstrual cycle)

• Proliferative phase (11 days): Occurs before ovulation. (but after the last cycle which desquamated the epithelium)

• Epithelial cells and stromal cells proliferate rapidly.– Due to the high levels of _estrogen_ secreted by the

ovaries.• The epithelial surface is re-epithelialized in 4-7 days.• By the end of this phase the endometrium has increased

greatly in thickness (up to 3-5 mm).• Increased number of stromal cells.• Progressive growth of endometrial glands which produce a

stringy mucus used to guide spermatozoa.

Sherwood’s Human Physiology 20-15 5th Ed. & 20-16 6th Ed.

The Endometrial Cycle (Menstrual cycle)

Sherwood’s Human Physiology 20-15 5th Ed. & 20-16 6th Ed.

• Secretory phase (12 days): Occurs after ovulation.

• Slight proliferation of the endometrium (5-6 mm).

• Due to the corpus luteum secretion of estrogens.

• Swelling and increased secretion of the endometrium.

• Due to the corpus luteum secretion of progesterone.

The Endometrial Cycle (Menstrual cycle)

Sherwood’s Human Physiology 20-15 5th Ed. & 20-16 6th Ed.

• The glands increase in tortuosity.

• Excessive secretion accumulates.

• Stromal cells have large cytoplasms full of glycogen and lipids.

• The blood supply increases & vessels increase in tortuosity.

• The whole purpose for these endometrial changes is to accommodate a fertilized ovum. Usually 3-4 days after ovulation.

The Endometrial Cycle (Menstrual cycle)

Guyton’s Textbook of Medical Physiology 81-7

• Menstrual Phase (5 days):• If no ovum is fertilized about day 26 the corpus luteum involutes

and estrogen and progesterone levels fall.• The decrease in estrogen and progesterone levels induce

menstruation.– Decreased stimulation of the endometrial cells.– Involution of endometrial cells.

• Tortuous blood vessels become vasospastic, resulting in hemorrhage and necrosis of the tissues.

• Eventually the necrotic layers separate from the uterus until all the superficial layer of the endometrium have desquamated.

• The mass is expelled due to uterine contractions. Within 4-7 days after menstruation starts the loss of blood stops as the endometrium has re-epithelized.

Hormonal Regulation of the Endometrial Cycle

• Postovulatory phase

– High levels of estrogen and progesterone secretion by the corpus luteum and secretion of inhibin have negative feedback control (on both anterior pituitary and hypothalamus) over the secretion of FSH and LH.

Guyton’s Textbook of Medical Physiology 81-3

Hormonal Regulation of the Endometrial Cycle

• Follicular growth phase– 3 days before menstruation estrogen, progesterone,

and inhibin levels decrease, releasing their control over the anterior pituitary and hypothalamus. FSH and LH levels increase.

– New follicle growth induces estrogen secretion slowly inhibiting FSH and LH production.

– (Does not explain preovulatory surge in LH and FSH?)

Guyton’s Textbook of Medical Physiology 81-3

Guyton’s Textbook of Medical Physiology 81-3

Hormonal Regulation of the Endometrial Cycle

• Preovulatory phase

– It is believed that the high levels of estrogen or the beginning of progesterone secretion is responsible for a positive feedback resulting in a surge of LH and FSH production.

Guyton’s Textbook of Medical Physiology 81-3

Hormonal Regulation of the Endometrial Cycle

Sherwood’s Human Physiology 20-18 5th Ed.& 20-19 6th Ed.

Summary

Sherwood’s Human Physiology 20-15 5th Ed. & 20-16 6th Ed

• Follicular (O) & Proliferative (U) Phase• Increasing E (from follicle) leading to a peak before ovulation, decreasing FSH

• Ovulation• E drop followed by LH & FSH surge and P increase

• Luteal (O) & Secretory (U) Phase• E & P increase, LH & FSH decrease

• Beginning of New Follicular (O) & Menstrual (U) Phase

• E & P decrease, LH & FSH increase

Non-Ovarian Cycle Functions of Estrogen & Progesterone

• Progesterone functions in breast development & and is mainly involved in pregnancy.

• Estradiol (the principal estrogen) is involved in development of the secondary sex characteristics of the female.– Increased size of the reproductive organs– Increases osteoblast activity and therefore bone

growth– Increases total body protein– Slightly increase metabolic rate– Development of a soft & smooth skin